1. Field of the Invention
The present invention relates to a device for protecting an electronic circuit and a method for forming such a device.
2. Description of the Related Art
Many electronic circuits, for example for cell phones, are formed by attaching to a main support, generally called a motherboard, elementary electronic circuits formed separately, each fulfilling a specific function. As an example, for a cell phone, an elementary electronic circuit corresponds to a radio transceiver circuit, to be connected to the cell phone antenna, which demodulates the signals received at the antenna level and modulates the signals to be transmitted. Another elementary electronic circuit corresponds to a power amplifier circuit for amplifying the signals to be transmitted provided by the radio transceiver circuit. Each elementary electronic circuit is formed on a distinct support, for example, a ball grid array (BGA) or a land grid array (LGA) casing.
Some elementary electronic circuits may be sensitive to electromagnetic disturbances. Such is the case, for example, for the radio transceiver circuit of a cell phone which is generally attached to the motherboard, like the power amplifier circuit, close to the antenna. In particular, the proper operation of the radio transceiver circuit may be disturbed by the electromagnetic disturbances transmitted by the power amplifier circuit and other external circuits.
FIG. 1 shows a conventional example of protection of an elementary electronic circuit against electromagnetic disturbances. In FIG. 1, a portion of a motherboard 10 on which an elementary electronic circuit 12 is welded has been shown in cross-section view. As an example, elementary electronic circuit 12 is formed of a BGA package 14, welded to motherboard 10 via bumps 16. Elementary electronic circuit 12 comprises an integrated circuit 18, attached to package 14 by a glue layer 20. Electric wires 22, for example, made of gold, ensure an electric connection between chip 18 and BGA package 14. A resin block 24 covers integrated circuit 18 and protects it against mechanical shocks.
To protect integrated circuit 18 against electromagnetic disturbances, a metal cover 26, welded to motherboard 10 and which encapsulates circuit 12, is provided. Cap 26 is grounded via motherboard 10. Generally, it is necessary to provide a metal cover such as described in FIG. 1 for each elementary electronic circuit to be protected against electromagnetic disturbances.
The current tendency is to integrate on a same elementary electronic circuit several functions previously performed by separate elementary circuits. As an example, in mobile telephony, it may be desirable to form a single elementary electronic circuit which integrates the functions previously performed by the transceiver circuit and the power amplifier circuit. This may be obtained by arranging several integrated circuits on a same BGA package, a same LGA package, or another type of package.
A difficulty then is to protect certain components of such an elementary electronic circuit against electromagnetic disturbances transmitted by other components of the same elementary electronic circuit. Indeed, the arranging of metal covers directly at the level of the elementary electronic circuit is generally incompatible with conventional methods for manufacturing such circuits.